Improvements in and relating to the control of electric motors

1,078,972. Control of A.C. motors. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. May 7, 1964 [May 10, 1963], No. 18618/63. Heading H2J. The rotor circuit of an induction motor comprises bridge rectifier RB, the speed of the motor being reduced by stepwise increase of resistance R1-R3, whilst control of rectifier CR1 provides additional continuous regulation Capacitor C quenches alternately one of the rectifiers CR1, CR2, when the other rectifier is triggered. In another quenching arrangement, the triggering signals for rectifiers CR1, CR2 are obtained through blocking oscillators BO1 BO2, connected to multivibrator MV. Oscillators BO1, BO2 produce triggering signals corresponding to the leading and trailing edges respectively of the output wave from the multivibrator. When a D.C. signal at terminal T6 is zero, the multivibrator is free-running, the rectifier CR1 determining a mean current corresponding to one half of the normal current in the rotor circuit. The conducting periods of the rectifier CR1 are lengthened or shortened by applying positive or negative signals to the terminal T6.